Light emitting diode module with three part color matching

ABSTRACT

A light emitting diode module is produced using at least one LED and at least two selectable components that form a light mixing chamber. First and second selectable components have first and second types of wavelength converting materials with different wavelength converting characteristics. The first and second wavelength converting characteristics alter the spectral power distribution of the light produced by the LED to produce light with a color point that is a predetermined tolerance from a predetermined color point. Moreover, a set of LED modules may be produced such that each LED module has the same color point within a predetermined tolerance. The LED module may be produced by pre-measuring the wavelength converting characteristics of the different components selecting components with wavelength converting characteristics that convert the spectral power distribution of the LED to a color point that is a predetermined tolerance from a predetermined color point.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/534,661, filed Jun. 27, 2012, which, in turn, is a divisional of U.S.application Ser. No. 12/617,668, filed Nov. 12, 2009, now U.S. Pat. No.8,220,971, which, in turn, claims the benefit of U.S. ProvisionalApplication No. 61/117,060, filed Nov. 21, 2008, all of which areincorporated by reference herein in their entireties.

FIELD OF THE INVENTION

This invention relates to the field of general illumination, and morespecifically, to illumination devices using semiconductor based lightingelements such as light emitting diodes (LEDs).

BACKGROUND

The use of light emitting diodes in general lighting is still limiteddue to limitations in light output level or flux generated by theillumination devices. Limits in flux are due to the limited maximumtemperature of the LED chip, and the life time requirements, which arestrongly related to the temperature of the LED chip. The temperature ofthe LED chip is determined by the cooling capacity in the system, andthe power efficiency of the device (optical power produced by the LEDsand LED system, versus the electrical power going in). Illuminationdevices that use LEDs also typically suffer from poor color qualitycharacterized by color point instability. The color point instabilityvaries over time as well as from part to part. Poor color quality isalso characterized by poor color rendering, which is due to the spectrumproduced by the LED light sources having bands with no or little power.Further, illumination devices that use LEDs typically have spatialand/or angular variations in the color. Additionally, illuminationdevices that use LEDs are expensive due to, among other things, thenecessity of required color control electronics and/or sensors tomaintain the color point of the light source or using only a smallselection of produced LEDs that meet the color and/or flux requirementsfor the application.

Consequently, improvements to illumination device that uses lightemitting diodes as the light source are desired.

SUMMARY

A light emitting diode module is produced using at least one lightemitting diode (LED) and at least two selectable components that are apart of a light mixing chamber that surrounds the LEDs and includes anoutput port. A first selectable component has a first type of wavelengthconverting material with a first wavelength converting characteristicand a second selectable component has a second type of wavelengthconverting material with a different wavelength convertingcharacteristic. The first and second wavelength convertingcharacteristics alter the spectral power distribution of the lightproduced by the LED to produce light through the output port that has acolor point that is a predetermined tolerance from a predetermined colorpoint. Moreover, a set of LED modules may be produced such that each LEDmodule has the same color point within a predetermined tolerance. TheLED module may be produced by pre-measuring the wavelength convertingcharacteristics of the different components selecting components withwavelength converting characteristics that convert the spectral powerdistribution of the LED to a color point that is a predeterminedtolerance from a predetermined color point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of an embodiment of a lightemitting diode module.

FIG. 2 illustrates a perspective, exploded view of the LED module fromFIG. 1.

FIG. 3 illustrates a cross-sectional view of an embodiment of the lightmixing chamber of the LED module of FIG. 1 with multiple sidewallinserts and windows.

FIG. 4 shows a (u′v′) chromacity diagram, which is also known as the CIE1976 UCS (uniform chromacity scale) diagram.

FIG. 5 illustrates example target color points and tolerance metrics onthe CIE 1976 UCS diagram.

FIG. 6 is a flow chart illustrating the part of the assembly process foran LED module.

FIG. 7 is a diagram illustrating color points of LED modules andpredetermined targets on the black-body curve from the CIE 1960 diagramwhere the X axis represents CCT and the Y axis represents the degree ofdeparture (Δuv) from the black-body curve.

FIG. 8 illustrates a set of LED modules that all produce the same colorpoint within a predetermined tolerance using wavelength convertingcomponents having differing wavelength converting characteristics.

FIG. 9 illustrates a board with a plurality of packaged LEDs havingdiffering wavelengths.

DETAILED DESCRIPTION

FIG. 1 illustrates a perspective view of an embodiment of a lightemitting diode (LED) module 100 and FIG. 2 illustrates a perspective,exploded view of the LED module 100. It should be understood that asdefined herein an LED module is not an LED, but is an LED light sourceor fixture or component part of an LED light source or fixture andcontains an LED board, which includes one or more LED die or packagedLEDs. The LED module 100 is similar to the LED illumination devicedescribed in U.S. Ser. No. 12/249,874, entitled “Illumination Devicewith Light Emitting Diodes”, filed Oct. 10, 2008, by Gerard Harbers,which has the same assignee as the present application and the entiretyof which is incorporated by reference herein.

The LED module 100 includes a base 110 and a top section 120, which maybe manufactured from highly thermally conductive material, such as analuminum based material. The base 110 includes a board 112 with aplurality of LEDs 114 that may be symmetrically arranged. In oneembodiment, the LEDs 114 are packaged LEDs, such as the Luxeon Rebelmanufactured by Philips Lumileds Lighting. Other types of packaged LEDsmay also be used, such as those manufactured by OSRAM (Ostar package),Luminus Devices (USA), or Tridonic (Austria). As defined herein, apackaged LED is an assembly of one or more LED die that containselectrical connections, such as wire bond connections or stud bumps, andpossibly includes an optical element and thermal, mechanical, andelectrical interfaces. The LEDs 114 may include a lens over the LED die.Alternatively, LEDs without a lens may be used. The board 112 provideselectrical and thermal contact with the LEDs 114. The board 112 is alsoin thermal contact with the base 110, which acts as a heat sink. Theboard may be an FR4 board, e.g., that is 0.5 mm thick, with relativelythick copper layers, e.g., 30 μm to 100 μm, that serve as thermalcontact areas. Alternatively, the board 104 may be a metal core printedcircuit board (PCB) or a ceramic submount with appropriate electricalconnections. Other types of boards may be used, such as those made ofalumina (aluminum oxide in ceramic form), or aluminum nitride (also inceramic form). The board 112 may include a reflective top surface or areflective plate 113 may be mounted over the top surface of the board112. The reflective plate 113 may be made manufactured from a materialwith high thermal conductivity, such as an aluminum based material thatis processed to make the material highly reflective and durable. By wayof example, a material referred to as Miro®, type Miro 27 Silver,manufactured by Alanod, a German company, may be used.

If desired, the base 110 may be produced from multiple pieces. Forexample, the base 110 may include a lower section 116 through whichelectrical connection to the board 112 is made and an upper section 118that is attached to the lower section 116, e.g., by screws 117 (shown inFIG. 1), bolts, or other appropriate attachment mechanism. The uppersection 118 may include an aperture 119 into which the board 112 andLEDs 114 extends.

The top section 120 includes a center aperture 122 that extends throughthe top section 120. The top section 120 is attached to the base 110 byscrews 124, bolts, or other appropriate attachment mechanism. Forexample, the top section 120 may be screwed onto the base 110 ifdesired. An output port is defined by the center aperture 122 and iscovered with a window 130 that is mounted to the upper surface of thetop section 120, e.g., by epoxy, silicone or other appropriateattachment mechanism. The window 130 may be transparent or translucentto scatter the light as it exits. The window 130 may be manufacturedfrom an acrylic material that includes scattering particles, e.g., madefrom TiO2, ZnO, or BaSO4, or other materials that have low absorptionover the full visible spectrum. In another embodiment, the window 130may be a transparent or translucent plate with a microstructure on oneor both sides. By way of example, the microstructure may be a lensletarray, or a holographic microstructure. Alternatively, the window 130may be manufactured from AlO₂, either in crystalline form (Sapphire) oron ceramic form (Alumina), which is advantageous because of its hardness(scratch resistance), and high thermal conductivity. The thickness ofthe window may be between e.g., 0.5 and 1.5 mm. If desired, the windowmay have diffusing properties. Ground sapphire disks have good opticaldiffusing properties and do not require polishing. Alternatively, thediffuse window may be sand or bead blasted windows or plastic diffusers,which are made diffusing by dispersing scattering particles into thematerial during molding, or by surface texturing the molds.

A sidewall insert 126 may be positioned within the center aperture 122of the top section 120 to define the sidewalls. Alternatively, thesidewalls may be defined by the walls of the aperture 122 itself. Thesidewall insert 126 may be, e.g., manufactured from a material referredto as Miro®, type Miro 27 Silver, manufactured by Alanod, a Germancompany. The sidewall insert 126 may be produced as a strip of materialthat is bent to form a ring shape. When assembled, a light mixingchamber 101 is defined by the sidewalls of the center aperture 122 ofthe top section 120, e.g., the sidewall insert 126, along with thewindow 130 and the reflective bottom surface, e.g., the reflective plate113 on the board 112 of the base 110, which are, therefore, sometimescollectively referred to as components of the chamber 101.

The light mixing chamber 101 of the LED module 100 may be formed fromdifferent or additional components. For example, as illustrated incross-sectional view in FIG. 3, the light mixing chamber 101 of the LEDmodule 100 is illustrated as being formed from the reflective plate 113,two sidewall inserts, a top sidewall insert 126 and a bottom sidewallinsert 127, and two windows, a top window 130 and a bottom window 131.

At least two of the components of the chamber 101 are coated orimpregnated with different wavelength converting materials, and aresometimes referred to herein as wavelength converting components. Thedifferent types of wavelength converting materials on the wavelengthconverting components have different wavelength convertingcharacteristics. By way of example, the window 130 may be coated with afirst type of wavelength converting materials 132 that, e.g., convertsblue light to yellow light, while the sidewall insert 126 may be coatedwith second type of wavelength converting material 128 that, e.g.,converts blue light to red light. In one embodiment, the sidewall insert126 is not used and the sidewalls of the center aperture 122 are coatedwith a wavelength converting material. If desired, the reflective plate113 may be coated with wavelength converting material that may be thesame or differ from the other wavelength converting materials on otherwavelength converting components. If desired, the top and bottomsidewall inserts 126, 127 and/or windows 130, 131 (FIG. 3) may be coatedwith different wavelength converting materials. Thus, a portion of theconverted light from window 130 will be transmitted into the lightmixing chamber 101 through the bottom window 131.

The wavelength converting materials may be phosphor or luminescent dyes,which will be generally referred to herein as phosphor for the sake ofsimplicity. By way of example, the phosphors used as the wavelengthconverting materials may be chosen from the set denoted by the followingchemical formulas: Y₃Al₅O₁₂:Ce, (also known as YAG:Ce, or simply YAG),Lu₃Al₅O₁₂ (also known as LuAG:Ce, or simply LuAG), (Y,Gd)₃Al₅O₁₂:Ce,CaS:Eu, SrS:Eu, SrGa₂S4:Eu, Ca₃(Sc,Mg)₂Si₃O₁₂:Ce, Ca₃Sc₂Si₃O₁₂:Ce,Ca₃Sc₂O₄:Ce, Ba₃Si₆O₁₂N₂:Eu, (Sr,Ca)AlSiN₃:Eu, CaAlSiN₃:Eu. The phosphoror combination of phosphors may be mixed as a dispersion in a binder forapplication to a surface by spray painting, screen printing, stenciling,or doctor blading techniques. These techniques are useful to depositsmall dots of phosphor, stripes of phosphor, or to uniformly coat thesurface. Alternatively, the phosphor or combination of phosphors mayalso be mixed in powder form with small pellets of binding material forapplication to a surface, e.g., by spraying or by application of anelectric field, as part of a powder coating process. The small pelletshave a low melting point and uniformly coat the surface when heated tothe melting point of the binder.

With the two or more of wavelength converting components of the lightmixing chamber 101 each with different wavelength converting properties,the LED module 100 may produce a predetermined or target color pointwith a high degree of accuracy.

FIG. 4 shows a (u′v′) chromacity diagram, which is also known as the CIE1976 UCS (uniform chromacity scale) diagram. The CIE 1976 UCS diagramillustrates the chromacities of a black-body radiator by curve 200,which is sometimes referred to as the Planckian locus. Ideally, lightsources produce light that lies on the black-body curve 200 at a targetcolor point. In practice, however, producing light at a target colorpoint on the black-body curve 200 is difficult, particularly with an LEDlight source because of the lack of precise control over the lightoutput of an LED light source manufactured using current processes.Typically, there will be some distance between the color point of thelight produced by the light source and the target color point on theblack-body curve 200, which is known as the degree of departure from thetarget color point on the black-body curve. In the context of the CIE1976 UCS diagram illustrated in FIG. 4, target color points 256-258 areillustrated as exemplary target color points and the degree of departurefrom the target color point is referred to in units of Δu′v′. When thecolor point of a light source varies significantly from a predeterminedtarget color point, the color of the light will be perceptivelydifferent from the desired color. Moreover when light sources are neareach other, e.g., in accent lighting or a display, even slight colordifferences are noticeable and considered undesirable. One measure ofvariation from a target color point is the MacAdam ellipse. The MacAdamellipse generally refers to a region on a chromaticity diagram thatcontains all colors that are indistinguishable to the average human eyefrom the color at the center of the ellipse. The MacAdam ellipse isbased on empirically based “just noticeable differences” between colors.Because the human eye is more sensitive to some colors than others, thesize of the MacAdam ellipse may differ depending on its location in thechromaticity space. FIG. 5 illustrates 1, 2, 3, and 4 step MacAdamellipses 250, 252, and 254 around target color points 256, 257, and 258,respectively, in a u′v′ CIE 1976 UCS diagram. Another measure ofvariation from a target color point is a degree of departure Δu′v′ fromthe target color point. For example, the target color point may be colorpoint 256 on the black-body curve and all color points within circle 251exhibit a degree of departure Δu′v′ that is less than 0.0035. Similarly,circles 253 and 255 illustrate degrees of departure less than 0.0035about target color points 257 and 258, respectively. As can be seen inFIG. 5, a degree of departure Δu′v′ that is less than 0.0035 isapproximately equivalent to a two-step MacAdam ellipse, illustrated bythe lighter circles. Circle 259 illustrates a degree of departure Δu′v′that is less than 0.009 about color point 257. Thus, the specificationfor color of light output by LED module 100 can be expressed as a colorwithin a predetermined tolerance of a target color point. For example,LED module 100 may achieve a particular target color point within atwo-step MacAdam ellipse. In another example, LED module 100 may achievea particular target color point within a degree of departure Δu′v′ lessthan 0.009. Both larger and smaller predetermined tolerance levels maybe achieved with LED module 100 if desired.

An LED is typically binned after a production run based on a variety ofcharacteristics derived from their spectral power distribution. The costof the LEDs is determined by the size (distribution) of the bin. Forexample, a particular LED may be binned based on the value of its peakwavelength. The peak wavelength of an LED is the wavelength where themagnitude of its spectral power distribution is maximal. Peak wavelengthis a common metric to characterize the color aspect of the spectralpower distribution of blue LEDs. Many other metrics are commonly used tobin LEDs based on their spectral power distribution (e.g. dominantwavelength, xy color point, uv color point, etc.). It is common for blueLEDs to be separated for sale into bins with a range of peak wavelengthof five nanometers.

As discussed above, LED module 100 includes a board 112 with a pluralityof LEDs LEDs 114. The plurality of LEDs 114 populating board 112 areoperable to produce light with a particular spectral power distribution.The color aspect of this spectral power distribution may becharacterized by its centroid wavelength. A centroid wavelength is thewavelength at which half of the area of the spectral power distributionis based on contributions from wavelengths less than the centroidwavelength and the other half of the area of the spectral powerdistribution is based on contributions from wavelengths greater than thecentroid wavelength. In some production examples, the centroidwavelengths for a plurality of boards each having a number of LEDs,e.g., eight LEDs, will differ by 1 nm or more. Where the boards arepopulated with LEDs carefully selected for their close to matchingspectral power distribution or with LEDs from a small bin, the centroidwavelengths will differ by 0.5 nm or more. Of course, costs increasesignificantly by producing boards with a closely matched centroidwavelengths.

The LED module 100 can accommodate LEDs with a wide spectral powerdistribution while still achieving a target color point within apredetermined tolerance. Moreover, multiple LED modules 100 may beproduced, each with one or more LEDs having different spectral powerdistributions, e.g., a deviation in centroid wavelengths of 0.5 nm to1.0 nm or more, while still achieving closely matched color points fromone LED module 100 to the next and, where the matching color points ofthe LED modules 100. Moreover, the color points from the LED modules 100may also be within a predetermined tolerance from a target color point.Thus, less expensive LEDs may be used. By using the two or moreselectable wavelength converting components of the light mixing chamber101, the color point of the light emitted by the LED module 100 may beaccurately controlled. For example, during assembly of the LED module100, the two or more wavelength converting components may be selectedbased on their wavelength converting characteristics and the spectralpower distribution of the light produced by the LEDs 114 so that theresulting light that is transmitted through the window 130 has a colorpoint that is within a predetermined tolerance of a predetermined targetcolor point. The wavelength converting components of the LED module 100may be selected to produce a desired degree of departure Δu′v′ ofbetween 0.009 and 0.0035 and smaller if desired, such as 0.002. Forexample, LED modules 100 having light sources with centroid wavelengthsthat differ by more than 1.0 nm may be produced using selectedwavelength converting components to produce a degree of departure ofΔu′v′ of 0.007 or less, such as 0.0035. Where LED modules 100 have lightsources with centroid wavelengths that differ by more than 0.5 nm, thewavelength converting components may be selected to produce a degree ofdeparture of Δu′v′ of 0.0035 or less.

The CIE 1960 UCS color space has generally been superseded by the CIE1976 UCS as an expression of uniform chromaticity space. However, theCIE 1960 UCS color space is still useful as an expression ofchromaticity because the isothermal lines of correlated colortemperature (CCT) are lines aligned perpendicular to the Planckianlocus. Producing a target color point is desirable for light sources ingeneral. For example, when used for purposes of general illumination, itis desirable that the LED module 100 produce white light with aparticular correlated color temperature (CCT). CCT relates to thetemperature of a black-body radiator and temperatures between 2700K and6000K are typically useful for general illumination purposes. Highercolor temperatures are considered “cool” as they are bluish in color,while lower temperatures are considered “warm” as they contain moreyellow-red colors. By way of example, CCTs of 2700K, 3000K, 3500K,4000K, 4200K, 5000K, 6500K on the black body curve or a CCT inilluminant series D are often desirable. In the context of the CIE 1960UCS diagram, the degree of departure is the distance between the colorpoint of the light produced by the light source and the Planckian locusalong a line of constant CCT. In the context of the CIE 1960 UCSdiagram, the degree of departure is referred to in units of Δuv. Thus,the color point of a white light source may be described as a CCT valueand a Δuv value, i.e., the degree of departure from the black-body curveas measured in the CIE 1960 color space. It follows that thespecification for color of light output by LED module 100 can beexpressed as a CCT value within a predetermined tolerance and a Δuvvalue within a predetermined tolerance.

FIG. 6 is a flow chart illustrating a part of the assembly process foran LED module 100. As illustrated in FIG. 6, a plurality of each of thewavelength converting components are produced with varying wavelengthconverting properties (302 and 304). If desired, the wavelengthconverting components may be produced by the entity that assembles theLED module 100 or by an external entity that then provides thewavelength converting components to the entity that assembles the LEDmodule 100. The different wavelength converting characteristics of thewavelength converting components are produced, e.g., by varying theconcentration and/or the thickness of the wavelength converting materialon or in the components. The concentration and/or the thickness of thewavelength converting material may be varied to produce components withwavelength converting characteristics that differ by 0.001 Δuv (in theCIE 1960 diagram) or less. For example, a plurality of windows 130 maybe produced, with different concentrations and/or thicknesses of yellowwavelength converting material 132. Similarly, a plurality of sidewallinserts 126 (or reflective plate 113) may be produced, with differentconcentrations and/or thicknesses of red wavelength converting material128. If desired, the same formulation of wavelength converting materialmay be used for each component, e.g., the sidewall inserts 126 orwindows 130, but with differing concentrations and/or thicknesses.Additionally, different formulations of wavelength converting materialmay be used, e.g., different mixtures of various wavelength convertingmaterials may be used. For example, the sidewall inserts 126 may becoated with a wavelength converting material 128 having differing ratiosof red and yellow phosphors with the same or different concentrationsand thicknesses. Similarly, different areas of the component may becoated with different wavelength converting materials. Further, the sameconcentration and thickness may be used, but with differing amounts ofcoverage area on the component, e.g., the amount of uncovered portion ofthe sidewall insert may vary.

The wavelength converting characteristics of the plurality of thewavelength converting components are measured (306 and 308). Thewavelength converting components are placed on a test fixture, whichincludes a light source, e.g., a board 112 with LEDs 114, that produceslight with a known spectral power distribution and color point. Thewavelength converting components are separately placed on the testfixture and the color point shift is measured using, e.g., aspectrometer and an integrating sphere. If desired, an intensitymeasurement using a dichroic filter can be done as well as or instead ofthe integrating sphere measurement, or a colorimeter such as produced byKonica-Minolta (CL-200 colorimeter) can be used. The measured wavelengthconverting characteristics for each component is stored. A selfreferencing measurement may be used for the wavelength convertingcharacteristics of the components. For example, color point produced bythe full spectral power distribution of the LEDs 114 and the measuredcomponent may be compared to the color point produced by the spectralpower distribution that excludes the wavelength converted light toproduce a self referencing Δuv value.

The color point shift of the wavelength converting components isillustrated in the CIE 1976 diagram of FIG. 4. The color point of thetest light source, which produces blue light at, e.g., 445 nm, isillustrated as point 210 in the diagram. The color point produced by,e.g., the wavelength converting material on or within the sidewallinsert 126 is illustrated as point 220, which corresponds with adominant wavelength of, e.g., 630 nm. The color point shift produced bythe sidewall insert 126 with the test light source is along the dottedline 222, where the amount of the shift will depend on the geometry ofthe light mixing chamber 101 and the thickness and/or concentration ofthe wavelength converting material 128 on the sidewall insert 126. Byway of example, the measured color point produced by one of the sidewallinserts 126 with the test light source is illustrated by point 224 andthe shift Δu′v′ from the color point produced by the test light sourcewithout the sidewall insert 126 (e.g., point 210) is illustrated by line226.

The color point produced by, e.g., the wavelength converting material onor within the window 130, is illustrated as point 230 which correspondswith a dominant wavelength of, e.g., 570 nm. The color point shiftproduced by a window 130 with the test light source is along the dottedline 232 depending on the thickness and/or concentration of thewavelength converting material 132 on the window 130. By way of example,the measured color point produced by one of the windows 130 with thetest light source is illustrated by point 234 and the shift Δu′v′ fromthe color point produced by the test light source without the window 130(e.g., point 210) is illustrated by line 236. If desired, differentformulations of the wavelength converting materials on a wavelengthconverting component may also be used, which would alter the color pointproduced by the wavelength converting materials (as illustrated by arrow240), and thus, the slope of the color point shift.

Typically, there is a difference in spectral power distribution from oneLED to the next. For example, LEDs that are supposed to produce bluelight at 452 nm will typically produce light that may range between 450nm and 455 nm or more. In another example, LEDs that are supposed toproduce blue light may produce light that ranges between 440 nm and 475nm. In this example, the spectral power distribution from one LED toanother may be as much as 8%. Accordingly, during the assembly process,the spectral power distribution and/or color point of the LEDs 114 inthe base 110 may be measured for each LED module 100 (310 in FIG. 6).The variation in the spectral power distribution of LEDs is one of thereasons why producing LED based light sources with consistent andaccurate color points is difficult. However, because the LED module 100includes two or more wavelength converting components with wavelengthconverting characteristics that can be individually selected,appropriate wavelength converting characteristics of the components canbe selected for a large variation of spectral power distributions ofLEDs 114 to produce a color point that is within a predeterminedtolerance, e.g., a Δu′v′ of less than 0.0035, from a target color point.The target color point may be, e.g., a CCT of 2700K, 3000K, 4000K, orother temperature on the black-body curve, or alternatively, the targetcolor point may be off of the black-body curve.

FIG. 7 is a diagram illustrating color points of LED modules andpredetermined target color points on the black-body curve from the CIE1960 UCS diagram where the X axis represents CCT and the Y axisrepresents the degree of departure (Δuv) from the black-body curve 400.The target color points may be, e.g., 4000K, 3000K and 2700K on theblack-body curve 400. Other target CCTs or color points off of theblack-body curve 400 may be used if desired. FIG. 7 illustrates apredetermined tolerance for each of the target color points with arectangle. For example, at the target color point at 4000K the CCT mayvary by ±90K, while at 3000K the CCT may vary by ±55K, and at 2700K theCCT may vary by ±50K. These predefined tolerances for CCT are within atwo step MacAdam ellipse centered on each respective target color pointon the black-body curve. The predetermined tolerance for the departurefrom the black-body curve Δuv for each CCT is ±0.001. In this example,Δuv may vary by a distance of 0.001 above the black-body curve 400(expressed as a positive tolerance value, +0.001) and may vary by adistance of 0.001 below the black-body curve 400 (expressed as anegative tolerance value, −0.001). This predetermined tolerance for Δuvis within a one step MacAdam ellipse centered on each respective targetcolor point on the black-body curve. The predetermined tolerances forCCT and Δuv illustrated in FIG. 7 is within a 2-step MacAdam ellipse andalso within the tolerance of Δu′v′ of 0.0035 shown in FIG. 5. The colorpoints within the illustrated tolerance from the target color points areso close that the color difference is indistinguishable for most peopleeven when the light sources are viewed side by side.

The diagram illustrates two color lines centered on the 3000K CCT forreference purposes. One color line 402 corresponds to the color pointshift produced by a first wavelength converting material. In the presentexample, color line 402 is a yellow phosphor coating on the window 130.Color line 404 corresponds to the color point shift produced by a secondwavelength converting material. In the present example, color line 404is a red phosphor coating on the sidewall insert 126. Color line 402indicates the direction of a shift in color point of light produced bythe yellow phosphor. Color line 404 indicates the direction of shift incolor point produced by the red phosphor. The first wavelengthconverting material and the second wavelength converting material areselected such that their respective directions of shift in color pointare not parallel. Because the direction of shift of the yellow phosphorand the red phosphor are not parallel, the direction of the color pointshift of light emitted by LED module 100 can be arbitrarily designated.This may be achieved by selecting the proper thickness and/orconcentration of each phosphor as discussed above. By way of example,the small spots, 412, 414, 416, and 418 graphically illustrate the colorpoints produced by one LED module 100 using different wavelengthconverting components. For example, spot 412 illustrates the color pointfor the LED module 100 with one set of wavelength converting components.By selecting a different window 130, the color point shifted for the LEDmodule 100 to spot 414. As can be seen, the difference in the colorpoints from spot 412 to 414 is parallel with the color line 402. Adifferent sidewall insert 126 is then selected to produce a color pointillustrated by spot 416. The difference in the color points from spot414 to 416 is parallel with the color line 404. While this is within the3000K target, an attempt to improve the color point by replacing thewindow 130 resulted in a color point illustrated by spot 418, where theshift between spot 416 and 418 is parallel with the color line 402. Byagain replacing the window 130 a color point of the LED module 100shifted along line 402 to produce a color point illustrated by largespot 420, which is well within the predetermined tolerance from thetarget color point of 3000K on the black-body curve.

The above example illustrates a trial and error approach to selectingthe appropriate wavelength converting components for a particular set ofLEDs 114 to produce an LED module 100 with a desired color point. With atrial and error approach, it is unnecessary to measure the spectralpower distribution of the light produced by the LEDs 114 beforeselecting the wavelength converting components. For example, a set ofwavelength converting components may be selected and combined with theLEDs 114 and the resulting color point measured. Adjustments of thewavelength converting components may then be made based on the measuredcolor point. However, in large scale production, it would be desirableto eliminate the trial and error approach. To eliminate the trial anderror approach, the spectral power distribution and/or color point ofthe LEDs 114 would be measured and the wavelength converting componentsmay then be appropriately selected to produce the target color pointwithin a predetermined tolerance. The selection may be made based on,e.g., a database generated from previous trials or based on mathematicalcalculations. It may be desirable to measure the light output after theLEDs 114 are combined with the selected wavelength converting componentsto ensure the light is within the predetermined tolerance of the targetcolor point, where one or both wavelength converting components may bechanged if the light output is out of tolerance. For this purpose it isbeneficial to label each module with a unique serial number, for examplein the form of a barcode which can easily be scanned in the productionprocess. It is beneficial to store in the database the spectral powerdensities of the board, and the final assembly, together with the typesof wavelength converting components used. This data is then used by analgorithm to suggest the wavelength components to be used to achieve thedesired performance of the modules.

With the two or more wavelength converting components selected, the LEDmodule 100 can then be assembled (314). As discussed above, the assemblymay include permanently attaching the base 110 with the reflective plate113, the top section 120 with sidewall insert 126 and the window 130,e.g., with bolts, screws, clamps, epoxy, silicon, or other appropriateattachment mechanisms. By repeating this process multiple times, aplurality of LED modules 100 may be produced with nearly identical colorpoints, e.g., each LED module 100 may produce a color point that differsfrom another by a predetermined tolerance, e.g., a Δuv of less than0.001.

Thus, the LED module 100 includes a means for converting the spectralpower distribution of the light emitting diodes to produce light fromthe light mixing chamber 101 with a color point within a degree ofdeparture Δu′v′ of 0.009 or smaller from a target color point in a CIE1976 u′v′ diagram. The means for converting the spectral powerdistribution includes a first means for converting the light produced bythe light emitting diodes to produce a color point shift of a firstmagnitude along a first direction in the CIE 1976 u′v′ diagram and asecond means for converting the light produced by the light emittingdiodes to produce a color point shift of a second magnitude along asecond direction in the CIE 1976 u′v′ diagram as illustrated in FIG. 4.As illustrated in FIG. 4, the first direction and the second directionare not parallel. Further, the first means and the second means areselectable to control their magnitudes in response to the spectral powerdistribution of the at least one light emitting diode to produce thedesired color point within an acceptable degree of departure. The firstmeans and second means for converting the light produced by the lightemitting diodes may be the two or more wavelength converting componentshaving differing wavelength converting characteristics and may be, e.g.,the reflective bottom surface 113, sidewall 128, or window 130 of theLED module. Alternatively, the first means and second means may belocated at the same position, e.g., both wavelength convertingcomponents are on the window 130, sidewall 128 or bottom surface 113.The wavelength converting components may be covered with or infused withwavelength converting materials, such as phosphor or luminescent dyes.Further, the wavelength converting components are selectable from aplurality of similar wavelength converting components that differ in thecoverage areas, concentration, and thickness of the wavelengthconverting materials to produce different magnitudes in the color pointshift in the CIE 1976 u′v′ diagram. The means for converting thespectral power distribution may also include a third or additional meansfor converting the light produced by the light emitting diodes thatdiffers from the first means and the second means. The means forconverting the spectral power distribution may incorporate the firstmeans and the second means into a single selectable component, e.g., thewindow 130, sidewall 128 or bottom surface 113. The inventors havedetermined that when separate selectable components are used, e.g., awindow 130 with a yellow phosphor and sidewall 128 with a red phosphor,approximately 10 different types of windows, i.e., 10 differentwavelength converting characteristics, and 5 to 10 different types ofsidewalls, i.e., 10 different wavelength converting characteristics, aregenerally adequate to produce the desired target color points with asmall degree of departure, e.g., Δu′v′ of 0.009 or less. Accordingly, ifthe first means and second means are to be located in one selectablecomponent, approximately 40 to 100 different selectable components wouldhave to be produced and kept in inventory. Further, by separating thefirst means and second means, higher efficiencies and color renderingindices are achievable. Alternatively, the first means and second meansmay be separate, but pre-assembled into one selectable component, e.g.,a window may be pre-assembled with a sidewall or bottom surface. Again,40 to 100 different pre-assembled components would have to be producedand kept in inventory to achieve the same possible variation as using 10types of a first means and 5-10 types of a separately selectable secondmeans.

FIG. 8 illustrates a set 500 of a plurality of LED modules 100 a, 100 b,100 c, and 100 d (collectively referred to sometimes as LED modules 100)that all produce the same color point within a predetermined tolerance,which can be accomplished as described above. To produce the same colorpoint, each of the LED modules 100 in the set 500 uses wavelengthconverting components with different wavelength convertingcharacteristics based on the spectral power distribution of the LEDs 114in the LED modules 100. By way of example, at least one of the windows130 a, 130 b, 130 c, and 130 d, the sidewall inserts 126 (shown in FIG.2) or the reflective plate (shown in FIG. 2), may have differentwavelength converting characteristics as illustrated by the shading ofwindows 130 a, 130 b, 130 c, and 130 d. When installed, e.g., in adisplay, downlighting, or overhead lighting, the LED modules 100 a, 100b, 100 c, and 100 d will produce light with color points that aredifficult for a human observer to distinguish.

Additionally, if desired, different wavelength LEDs 114 may be used inan LED module to improve the color rendering index (CRI). When all theLEDs 114 in the LED module 100 have substantially the same peakwavelengths, e.g., all the LEDs 114 are from the same bin having a binsize of 5 nm (for example a bin that includes 450 nm to 455 nm), a CRIvalue between, e.g., 75-85 may be achieved for an LED module 100 withCCTs of 2700K, 3000K, and 4000K, when a yellow (YAG) phosphor is used onthe window 130 and red phosphor with a peak wavelength of 630 nm is usedon the sidewall insert 126. However, by replacing one or more of theLEDs 114 with LEDs from a different bin so that the peak wavelengthdiffers from the peak wavelength of LEDs 114 by 10 nm or more, a higherCRI may be achieved. FIG. 9, by way of example, illustrates board 512with a plurality of packaged LEDs 514 each having a peak wavelength of,e.g., 452 nm and a second plurality of LEDs 515, each having a peakwavelength that is more than 10 nm greater than the wavelength of LEDs514. By way of example, the peak wavelength of the LEDs 515 may bebetween, e.g., 470 nm and 510 nm. As illustrated in FIG. 9, the LEDs 515are symmetrically arranged on the board 512 if possible. The board 512with LEDs 514 and 515 may be used in place of board 112 shown in FIG. 2.Compared to a board with LEDs that all have the same 452 nm peakwavelength, board 512 achieves a higher CRI value. By way of example, anLED module 100 having a CCT of 2700K, 3000K or 4000K, may use five LEDs514 with a wavelength between 450 nm and 455 nm and three LEDs 515 witha wavelength of 500 nm to 510 nm to achieve a CRI of 95. The use ofhigher wavelength LEDs decreases efficiency, in terms of lumen out ofthe LED module divided by electrical power going in. Thus, the number ofLEDs 515 with different wavelengths and the particular wavelength of theLEDs 515 that are used is a balance of the target CRI value and thedesired efficiency for the LED module 100.

Additionally, phosphors may be used to produce high CRI values. A numberof these phosphors are typically not used with LEDs due to thesensitivity of their respective emission properties to heat. However,the phosphors on the wavelength converting components, particularly thewindow 130 and the sidewall insert 126, are physically distant from theheat producing LEDs 114. In addition, the top section 120 of the LEDmodule 100 is thermally coupled to the wavelength converting componentsand acts as a heat sink. Thus, the phosphors can be maintained at arelatively low temperature. For example, phosphors deposited directly onan LED source may reach temperatures in excess of 150 degreescentigrade, whereas the phosphors deposited on window 130 and sidewallinsert 126 typically reach temperatures of approximately 70 to 90degrees centigrade. As a result of the use of thermally sensitivephosphors LED module 100 may be tailored to produce a desired CRI value.For example, phosphors such asLa₃Si₆N₁₁:Ce,LaSi₃N₅,(Sr,Ca)AlSiN₃:Eu,CaAlSiN₃:Eu²⁺,(Sr,Ca)AlSiN₃:Eu²⁺,Ca₃(Sc,Mg)₂,Si₃O₁₂:Ce,Sr_(0.8)Ca_(0.2)AlSiN₃:Eu,CaSc₂O₄:Ce,(Sr,Ba)₂SiO₄:Eu²⁺,SrGa₂S₄:Eu²⁺,SrSi₂N₂O₂:Eu²⁺,Ca₃Sc₂Si₃O₁₂:Ce³⁺, Y_(3-x)Al₂Al₃O₁₂:Ce^(x+)and Lu_(3-x)Al₂Al₃A₁₂:Ce^(x+), can be used on wavelength convertingcomponents to produce CRI values of 80 and higher, or even 95 andhigher.

Although the present invention is illustrated in connection withspecific embodiments for instructional purposes, the present inventionis not limited thereto. It should be understood that the embodimentsdescribed herein may use any desired wavelength converting materials,including dyes, and are not limited to the use of phosphors. Variousadaptations and modifications may be made without departing from thescope of the invention. Therefore, the spirit and scope of the appendedclaims should not be limited to the foregoing description.

What is claimed is:
 1. A method of producing a light emitting diodemodule, the method comprising: selecting a first component from aplurality of first components configured to define a light mixingchamber in the light emitting diode module, wherein the plurality offirst components includes a first wavelength converting material andeach of the plurality of first components has a different knownwavelength converting characteristic; selecting a second component froma plurality of second components configured to further define the lightmixing chamber in the light emitting diode module, wherein the pluralityof second components includes a second wavelength converting materialand each of the plurality of second components has a different knownwavelength converting characteristic, wherein the first component andthe second components are selected based on a spectral powerdistribution of an at least one light emitting diode such that whencombined with the at least one light emitting diode the first componentand the second component convert the spectral power distribution of theat least one light emitting diode to produce light from the light mixingchamber with a color point within a predetermined tolerance of apredetermined color point; and assembling the selected first componentand the selected second component with the at least one light emittingdiode.
 2. The method of claim 1, further comprising measuring thespectral power distribution of the at least one light emitting diodeprior to selecting the first component and the second component andwherein selecting one of the plurality of first components with a firstwavelength converting characteristic and one of the plurality of secondcomponents with a second wavelength converting characteristic is basedon the measured spectral power distribution.
 3. The method of claim 1,further comprising: combining the selected first component and theselected second component with the at least one light emitting diode inthe light mixing chamber; measuring the color point of the lightproduced from the light mixing chamber after the selected firstcomponent and the selected second component are combined with the atleast one light emitting diode; selecting a different one of theplurality of first components based on the measured color point toproduce light from the light mixing chamber with the color point withinthe predetermined tolerance of the predetermined color point prior toassembling the selected first component and the selected secondcomponent with the at least one light emitting diode.
 4. The method ofclaim 1, wherein the first type of wavelength converting material of thefirst selectable component produces a color point shift along a firstdirection in a CIE 1976 u′v′ diagram and the second type of wavelengthconverting material of the second selectable component produces a colorpoint shift along a second direction in the CIE 1976 u′v′ diagram,wherein the first direction and the second direction are not parallel.5. The method of claim 1, wherein the light mixing chamber is formed ina housing, wherein assembling the selected first component and theselected second component with the at least one light emitting diodecomprises mounting the first selectable component and the secondselectable component to the housing.
 6. The method of claim 1, whereinthe predetermined tolerance is characterized by the distance between thecolor point and the predetermined color point in the CIE 1976 u′v′diagram as less than 0.0035.
 7. The method of claim 1, wherein thepredetermined color point is a color point of one of illuminant series Dand a black-body radiator with a temperature of one of 2700K, 3000K,3500K, 4000K, 4200K, 5000K, 6500K.
 8. The method of claim 1, wherein thelight mixing chamber comprises a reflective bottom surface thatsurrounds the at least one light emitting diode; at least one reflectivesidewall that surrounds the bottom surface and the at least one lightemitting diode, and a window that is coupled to the at least onereflective sidewall to form the output port.
 9. The method of claim 8,wherein each of the first selectable component and second selectablecomponent comprise at least one of the reflective bottom surface, the atleast one reflective sidewall, and the window.
 10. The method of claim9, wherein the at least one reflective sidewall is a sidewall insertthat is positioned within the light mixing chamber to form the at leastone reflective sidewall.
 11. The method of claim 9, wherein the firstselectable component is the window and the second selectable componentis the at least one reflective sidewall.
 12. The method of claim 1,wherein the first selectable component and second selectable componentcomprises a first window and a second window, wherein a portion ofconverted light from the second wavelength converting material on thesecond window is transmitted into the light mixing chamber through thefirst window.